Bryan Singer knows perfectly how fans are dissapointed with Rogue on the franchise...

Speak for yourself. Rogue was a wonderfully developed character in the series, but was completely mischaracterized in X3, which did a disservice to the character from the film and the character as a whole.

Bryan did a wonderful job displaying her cinematic arc in parallel to her origins in the comics and have no doubt he would have continued the growth in character had he not left.